Mobile terminals routinely communicate within a licensed spectrum via networks supervised by various cellular operators. The licensed spectrum, however, has a finite capacity and may become somewhat scarce as the number of mobile terminals that are configured to communicate within the licensed spectrum increases at fairly dramatic rates. As the demands placed upon the licensed spectrum by the various mobile terminals begin to saturate the licensed spectrum, the mobile terminals may experience increasing levels of interference or limited resources with the licensed spectrum potentially eventually becoming a bottleneck for such communications. Therefore, it may be necessary to enable cellular operations on license-exempt bands as well in suitable situations to help offload the traffic.
An increasing number of other network topologies are being integrated with cellular networks. For instance, there might already be some other network system or other cellular system operating in an unlicensed band. These other network topologies include, for example, wireless fidelity (WiFi) networks, ad hoc networks and various other local area networks. The terminals, either mobile or fixed, supported by these other network topologies may communicate with one another in an unlicensed spectrum, such as a licensed-exempt industrial scientific medical (ISM) radio band. The ISM radio band supports other non-cellular systems, such as WiFi systems operating in accordance with the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, ZigBee systems operating in accordance with the IEEE 802.15 standard, Bluetooth systems and universal serial bus (USB) wireless systems. In this regard, the ISM radio band may include the 2.4 GHz ISM band in which WiFi 802.11b and 802.11g systems operate and the 5 GHz ISM band in which WiFi 802.11a systems operate. Though cellular technologies have not generally been deployed in the ISM band, such deployment could be considered for local-area Long Term Evolution (LTE) cellular networks as long as they meet the regulatory requirements in country-specific ISM bands, e.g., Federal Communications Commission (FCC) in the United States. Another example of a license exempt band is TV White Space (TVWS), which has been investigated widely in the recent years due to the large available bandwidths at suitable frequencies (e.g., TV spectrum in the 54-698 MHz range in the U.S.) for different radio applications. In the United States, the FCC has regulated licensed or license-exempt TV bands for the secondary-system applications, e.g., cellular, WiFi, WiMax, etc., on TV Band Devices (TVBD).
In an instance in which an LTE system is deployed in a licensed band, the LTE system is typically designed for continuous transmission, since a corresponding network operator may need to buy a certain spectrum for the network operator's usage. However, in order to deploy an LTE system in a shared band without any modification, the LTE system may generally occupy the spectrum all the time, and may totally, or partially, block any other system's usage, which may be unfair and may violate a regulatory requirement of an unlicensed band.
In this regard, for LTE transmissions in an unlicensed band, the LTE may need to use frequency sharing or time sharing, or both schemes, in order to coexist with other systems in a fair manner.